Sand production from hydrocarbon producing wells is a common problem which can inhibit the flow of hydrocarbons and damage the well. To mitigate this problem, a sand screen may be deployed in the well which acts as a filter to resist ingress of particles above a certain diameter.
In order to protect the sand screen from hole collapse, in-situ geo-mechanical loads and stresses and in order to enhance its filtering function, it is known to add a “gravel pack” external to the screens to support the open hole formation rock structure in the well. A gravel pack is a plurality of gravel particles, which allow the flow of fluid therebetween but resist the flow of sand therebetween.
The delivery of chemical treatment agents is often done using coiled tubing injection strings. The chemicals delivered may be chosen for a number of different applications. One such application is to dissolve a filter cake which has been deposited during a drilling and completion process.
However a problem with such a delivery is that the chemicals will tend to act on the thinnest section of filter cake. Once this relatively thin section dissolves the treatment fluid(s) within the hole section will flow hydrostatically into the near well bore/reservoir and will not act on the remaining filter cake within the well.
In the presence of a gravel pack, application of chemicals using coil tubing strings to place the treatment in-situ to act on, for example, a filter cake, is particularly ineffective because it is often difficult for the chemicals to be directed at the filter cake due to much of the space being taken by the gravel pack. This is particularly so for the upper side of a horizontal well.